Induction motor control: multivariable analysis and effective decentralized control of stator currents for high performance applications

Adequate control of the stator currents is a fundamental requirement for several high-performance induction motor (IM) control schemes. In this context, classical linear controllers remain widely employed due to their simplicity and success in industrial applications. However, the models and methods commonly used for control design lack valuable information –which is fundamental to guarantee robustness and high performance. Following this line, the design and existence of linear fixed controllers is examined using individual channel analysis and design. The studies here presented aim to establish guidelines for the design of simple (time-invariant, low order, stable, minimum-phase and decentralized), yet robust and highperformance linear controllers. Such characteristics ease the implementation task and are well suited for engineering applications, making the resulting controllers a good alternative for the stator currents control required for high-performance IM schemes; e.g., field oriented, passivity-based and intelligent control. Illustrative examples are presented to demonstrate the analysis and controller design of an IM, with results validated in a real-time experimental platform. It is shown that it is possible to completely decouple the stator currents subsystem without the use of additional decoupling elements

Fault Estimation Methods for Semi-Active Suspension Systems

International audienceSemi-Active (SA) suspension systems aim to improve the stability and comfort of vehicles. Although they offer better performance than passive suspensions, the actuators such as magneto-rheological dampers are more susceptible to failure. Oil leakage is the most common fault, and its effect is a reduction of the damping force. The estimation of suspension faults can be used with a Fault Tolerant Control system to prevent handling and comfort deterioration. However, fault estimation schemes introduce additional challenges due to the damper non-linear dynamics and the strong influence of the disturbances (i.e the road profile). One of the first obstacles for appropriate damper fault detection is the modeling of the fault, which has been shown to be of multiplicative nature. However, many of the most widespread fault detection schemes consider additive faults due to mathematical convenience. Two complementary model-based fault estimation schemes for semi-active dampers are proposed: an observer-based approach, which is intended to estimate additive faults; and a parameter identification approach, which is intended to estimate multiplicative faults. The performance of these schemes is validated and compared through simulations using a pickup truck model. Early results shows that a parameter identification approach is more accurate in fault estimation, whereas an observer-based approach is less sensible to parametric uncertainty

Flux-torque cross-coupling analysis of FOC schemes: Novel perturbation rejection characteristics

Field oriented control (FOC) is one of the most successful control schemes for electrical machines. In this article new properties of FOC schemes for induction motors (IMs) are revealed by studying the cross-coupling of the flux-torque subsystem. Through the use of frequency-based multivariable tools, it is shown that FOC has intrinsic stator currents disturbance rejection properties due to the existence of a transmission zero in the flux-torque subsystem. These properties can be exploited in order to select appropriate feedback loop configurations. One of the major drawbacks of FOC schemes is their high sensitivity to slip angular velocity perturbations. These perturbations are related to variations of the rotor time constant, which are known to be problematic for IM control. In this regard, the effect that slip angular velocity perturbations have over the newly found perturbation rejection properties is also studied. In particular, although perturbation rejection is maintained, deviations to the equilibrium point are induced; this introduces difficulties for simultaneous flux and torque control. The existence of equilibrium point issues when flux and torque are simultaneously controlled is documented for the first time in this article

Structural robustness assessment of electric machine applications using individual channel analysis and design

Adequate control of three-phase machines, such as induction motors -IMs- and synchronous generators, is of paramount importance for the electric power industry. These are multivariable, non-linear systems. In this paper, the individual channel analysis and design framework is used to formally demonstrate that the electrical subsystems of the IM and of the permanent magnet SG, due to their inherent structural robustness, are the multivariable equivalent to stable, minimum-phase, single-input single-output systems. As a cnsequence, an adequate performance and robustness may be achieved through fixed, stable, minimum-phase, diagonal controllers –justifying the widespread use of control schemes based on fixed, classical linear controllers such as PI

The multivariable structure function as an extension of the RGA matrix: relationship and advantages

It is common practice to specify the performance of control design tasks in terms of an output response to a given input. In spite of a greater complexity, this is also the case for multivariable plants, where for clarity of performance specification and design remains desirable to consider the inputs and outputs in pairs. Regardless of the structure and internal coupling of the plant, it is convenient to establish if decentralized control is capable of meeting design specifications: the control structure will be easy to implement, economic (less programming burden upon implementation), and may provide further physical insight. In line with this, the analysis and design of decentralized controllers using the relative gain array (RGA) and the multivariable structure function (MSF) are presented for the general multivariable case. It is demonstrated that the RGA matrix can be expressed in terms of the MSF. Moreover, it is shown that the correct interpretation of the MSF offers significative advantages over the RGA matrix analysis. While the RGA offers insight about the adequate pairing of input-output signals in a multivariable system, the MSF, besides providing this information, plays a crucial role in the design of stabilizing controllers (and their requirements) and the subsequent robustness and performance assessment of the closed loop control system. Theoretical results are drawn for a general n×n plant, with examples from electrical power systems and laboratory tank processes included to illustrate key concepts

Semi active damping force estimation using L P V − H ∞ estimators with different sensing configurations

International audienceSemi-active suspension systems have become a widespread tool to improve the handling and comfort of vehicles. These systems require adjustable dampers as well as supplementary sensing elements. In addition to displacements and accelerations, some of the best performing approaches require knowledge of the semi active damper force. Since this variable can be difficult and expensive to measure, several estimation methods have been proposed. In this article, two Linear-Parameter-Varying (LPV-) filters are developed to estimate the Semi-Active (SA) damper force, considering two different combinations of sensing elements: the first configuration is more expensive, but potentially more accurate and reliable; whereas the second configuration is cheaper and arguably less reliable. Thanks to the use of LPV- theory, both filters are designed to account for the main nonlinear phenomena of SA dampers (i.e. saturation, hysteresis, etc.), as well as being quadratically stable, robust to the road disturbances and optimized to reduce the estimation error in a specified frequency band. Simulations and experimental data are used to assess the proposed estimators as well as a typical inverse-dynamics estimation approach. The results show that while both of the proposed estimators yield a good degree of accuracy, there are indeed fundamental differences depending on the available sensing elements; a conclusion which could be crucial to appropriately define the instrumentation of semi-active suspension systems

Turbojet Thrust Augmentation through a Variable Exhaust Nozzle with Active Disturbance Rejection Control

Turbojets require variable exhaust nozzles to fit high-demanding applications; however, few reports on nozzle control are available. The purpose of this paper is to investigate the possible advantages of an exhaust gas control through a variable exhaust nozzle. The control design method combines successful linear active disturbance rejection control (LADRC) capabilities with a loop shaping controller (LSC) to: (i) allow designing the closed-loop characteristics in terms of gain margin, phase margin and bandwidth, and (ii) increase the LSC disturbance rejection capabilities with an extended state observer. A representation of the nozzle dynamics is obtained from first principles and adapted to achieve a stream-velocity-based control loop. The results show that the resulting controller allows improving the expansion of the exhaust gas to the ambient pressure for the whole operating range of the turbojet, increasing the estimated thrust by 14.23% during the tests with experimental data

The cross-coupling of lateral-longitudinal vehicle dynamics: Towards decentralized Fault-Tolerant Control Schemes

Publication électronique en juillet 2017; publication au format papier en avril 2018. L'article final contient 17 pages.International audienceIn recent years there has been an increasing interest in improving vehicle characteristics through the use of Vehicle Control Systems (VCS). In particular, VCS for the lateral (steering) and longitudinal (velocity) dynamics are used to improve the handling properties of a vehicle. Nonetheless, the introduction of the additional elements required for implementing these control systems also increases the possibility of faults. This problem can be mitigated by using Fault Tolerant Control(FTC) systems. The most common approach for steering FTC design is based on the use of a linear Bicycle Model (BM). Using this model decentralized steering controllers can be designed. However, the BM lacks significant lateral and longitudinal cross-coupling dynamics. In fact, the steering and velocity control problem could be viewed as a multivariable cross-coupled problem. In this article VCS for the steering and velocity are designed. The resulting controllers are decentralized and capable of practically eliminating the cross-coupling. A further problem, which has not been widely reported, is the propagation of the failure of one subsystem to other subsystems. It is shown that when the Velocity Control System (VelCS) fails, then the steering subsystem has a degraded performance due to cross-coupling. The main contribution of this article consists in showing that it is possible to detect and accommodate a failure of the VelCS within the steering control system, i.e. without requiring communication among subsystems. This enables a fully independent operation even if faults occur, that is a Decentralized Fault-Tolerant Control Scheme